The nature of the production of foam-in-place packaging, and the development of automated machinery for producing foam-in-place bags, is thoroughly described in U.S. Pat. Nos. 4,800,708 and 4,854,109 which are assigned to the assignee of the present application and which are incorporated entirely herein by reference. Briefly, a foam-in-place bag is a product in which a small amount of a foamable composition is placed into a plastic bag as the bag is being formed from stock plastic material. If the bag containing the foamable composition is placed within a container such as a cardboard box within a short time after being formed, the rising foam will fill the container while surrounding whatever fragile object may be in the box. If the container is closed as the foam rises, the result will be a custom package providing excellent protection for the object.
As further described in U.S. Pat. No. 4,898,327 ("the '327 patent") by the inventors of the present application and assigned to the common assignee of this application, one of the problems in such automated systems for forming foam-in-place bags is that the foamable compositions generally tend to harden rather rapidly after the foaming process is initiated. U.S. Pat. No. 4,898,327 is likewise incorporated entirely herein by reference. Thus, a common cartridge is for hardened foam to build up on the exterior of the nozzle from which the foamable compositions are injected into a bag being formed. As set forth in the '327 patent one method of addressing this problem is to clean the injection tip with solvent on a regular basis. In particular, in the '327 patent, it was discovered that the use of a sintered metal tip for the injection cartridge provided a novel cleaning method when a combination of solvent and compressed air was directed through the sintered tip. The action of forcing solvent and air through the sintered tip creates a frothing action of the solvent which helps keep the tip clean.
Additionally, a novel system for pumping the solvent to the tip was disclosed and claimed in the '327 patent.
After repeated successful use of the apparatus described in the '327 patent, however, it has been determined that there exists a further problem not originally recognized, and indeed raised by the nature of the improvement. Specifically, the typically used valving rod in an injection cartridge will not always return to the exact same position at the tip. Thus, foam could still build up, even though the frothing solvent was being passed through the sintered tip. As another factor, cartridge manufacture is such that the position of the valving rod with respect to the tip may differ enough from cartridge to cartridge to cause similar problems.
Accordingly, there exist a need for an improved sintered tip to take into account the inexact tolerances and position of a valving rod in the cartridges improved according to the '327 patent.
Additionally, the pumping system described in the '327 patent, although useful, offered some complexities of manufacture and operation, that could desirably be improved upon.